Integrated Vertical flow Constructed Wetland is a special kind of ecological establishment for wastewater treatment which has fine removal efficiency, little investment, simple management, low cost for running and high ability for nitrogen removal.
It is generally considered that the competence of nitrogen removal in wetlands mostly depends on the nitrification-denitrification of microorganisms, but microbial denitrification needs electrons from organic matter, so organic matter becomes an important factor influencing the removal efficiency. Now much wastewater presents the characteric of low carbon but high nitrogen, which means that the removal ability of wetlands for nitrogen faces baptism. This paper investigated the removal efficiency and variation of nitrogen on the condition of low carbon but high nitrogen in influent, which will bring realism significance to understand the mechanism of nitrogen removal and to enhance the removal efficiency of wetlands.
This study took the down pond of Integrated Vertical flow Constructed Wetland as the object, via contrasting the removal efficiency and concentration of different nitrogen in effluent between the wetland with macrophytes and without, to study the influence of macrophytes to nitrification and denitrification. By controlling the concentration of carbon and nitrogen in influent and measuring the nitrogen concentration in effluent to probe into the removal efficiency of wetlands under the condition of different nitrogen concentration in influent. Via observing the removal efficiency to nitrogen under the condition of C/N less than 1, measuring the intension
of nitrification and denitrification, variation tendency of different nitrogen, combining with quantity analysis of carbon, educed that it was likely to exist a denitrification approach needing no carbon in wetlands except the traditional nitrification and denitrification approach, which is the ANAMMOX approach. The results of this paper were as follows:
That pollutants directly absorbed by macrophytes were limited in wetlands, so the ability of nitrogen removal mostly depends on the nitrification and denitrification of macroorganisms. Macrophytes had no obvious influences to removal efficiency of ammonia nitrogen, but the influences to total nitrogen was very notable. Cumulation phenomena of nitrate nitrogen in wetlands without macrophytes was remarkable. When total nitrogen concentration was 6.4 mg/L around, nitrate nitrogen concentration in effluent could reach 2.83 mg/L, higher a magnitude than that in wetland with macrophytes. Macrophytes had no obvious influences to nitration rate while the influences to denitration rate was very obvious. Denitration rate and removal efficiency of total nitrogen in wetlands with macrophytes were more 1.4 and 1.7 times than that in wetlands without macrophytes respectively. Only limited oxygen was transmited to substrate inner via macrophytes radicle, so no material influences to the nitrification appeared in wetlands, but radicle could enhance the permeability of substrate and improve the stability of wetlands, and it also provides huge surface for macroorganisms to inhabit.
Wetlands presented better removal efficiency to high concentration ammonia in summer, and which was not influenced by organic matter or macrophytes. When concentration of ammonia nitrogen was 50.5 mg/L around, which in effluent could reduce to 1.5 mg/L with removal efficiency of 95%; When concentration of ammonia nitrogen rose to 100.5 mg/L, concentration in effluent could maintain about 10 mg/L with removal efficiency of 90%, which means that bacterias for nitrification and denitrification have strong tolerance to high concentration ammonia. When ammonia concentration in influent ranged from 5.5 mg/L to 50.5 mg/L, concentration in effluent behaved linearity relation with it(the value of R2 reaching 0.9971). When ammonia concentration in influent ranged from 0.5 mg/L to 50.5 mg/L, the quantity of total
nitrogen removed by wetlands behaved linearity relation with it(the value of R2 reaching 1).
Removal efficiency of nitrogen highly achieved 86.3% when value of C/N was less than 1, as much as which in wetlands with ample carbon source, while concentration variation of nitrate nitrogen had great difference. Concentration of nitrate nitrogen in effluent from wetlands with ample carbon was evidently low and the fluctuation was also little. Concentration of nitrate nitrogen in effluent from wetlands with scant carbon was very high early, even higher a magnitude than that from wetlands with ample carbon, then it played down to the level of former gradually. Via detection of denitrifing rate in wetlands and quantity analysis of carbon, it was found that neither full-denitrification nor short-denitrification could explains the results of experiment, so a denitrification approach needing no carbon was deduced to exist in wetlands. Ammonia nitrogen was oxidized to nitrite nitrogen, then nitrite nitrogen oxidized ammonia nitrogen into nitrogen gas, which was called ANAMMOX. This approach could not only explain the result of experiment, but also does not conflict with traditional nitrification and denitrification theory.
Carbon source had no obvious influences on nitrification, but which restricted the dinitrification observably. The ANAMMOX approach was very possible to exist in wetlands, which needs no carbon source and is difficult to be measured via traditional method.